Benzene and Natural Gas Production

Transcription

1 Benzene and Natural Gas Production 7/19/ S.E. Southwell, Editor Recently, there has been a lot of concern about the release of benzene in connection with natural gas production in the Barnett Shale. While the known carcinogen, benzene certainly is certainly one issue, it is not the only one for those concerned with urban gas drilling and production. Although recent air studies generally rate the majority of natural gas facilities in the Barnett Shale as having emission levels below limits, there are enough examples of sites exceeding long term safe levels to give pause to those people down-wind and in close proximity. However, the good news is that because the data show so many sites with low emissions, and because we know what types of things cause excessive emissions, it should be relatively easy to fix the problems. The industry has begun to give the problem attention, and local and state government can draw on those best practices to implement reasonable rules that would drastically reduce the chances of a large emissions event, or chronic excursions beyond safe limits. The topic at hand is one that tends toward misinformation, so we have included lots of footnotes here to reputable sources where the reader can learn more. We have tried to make the document understandable to a non-technical reader, while still leaving in enough technical information to back up the concepts presented. Facts about Benzene Benzene is a clear, sweet-smelling liquid hydrocarbon with formula C 6 H 6 formed in a ring. Benzene is a natural component of petroleum, and is used as an additive to gasoline for its anti-knock properties. Benzene is also widely used in industry, as one of the top 20 chemicals produced. In 2004, benzene constituted about 1% of the average gasoline formulation, but under rules implemented in 2007 by the EPA, that amount is scheduled to drop below 0.62%, with no formulation allowed to exceed 1.3%. 1 This reformulation could account for a large part of the decline in ambient benzene levels over the past few years. This was the case when California reformulated its gasoline in In Texas, the amount of benzene allowed to be emitted into the air is regulated by the Texas Commission on Environmental Quality (TCEQ), which examines scientific evidence to determine ambient levels that it considers safe. These levels, which are called Effects Screening Levels, or ESLs, are set for both short-term and long-term exposures. ESLs for benzene are in the microgram-per-cubic meter (µg/m 3 ) and parts-per-billion (ppb) range. Benzene Effects Screening Levels 3 : Short Term ESL : 180 ppb or 580 µg/m 3 (180 parts per billion or 580 micrograms per cubic meter) Long Term ESL: 1.4 ppb or 4.5 µg/m 3 (1.4 parts per billion or 4.5 micrograms per cubic meter) Short term ESL is the acure ReV, and long-term is the chronic ESL linear(c) 1

2 To put in perspective, what a part per billion (ppb) is, one part per million (ppm) is approximately two teaspoons of vapor inhaled daily for the average person 4. A part per billion would be one onethousandth of that. EPA estimates that 4 ppb exposure to benzene, over a lifetime would result in up to one extra case of leukemia in 10,000 people exposed, with latency of 5 to 15 years. 5 As another example to put these amounts in perspective, for a 1500 square foot house, typical of my neighborhood, the short term ESL for the volume of indoor air would be equivalent to having about 0.16 milliliters of evaporated benzene in the air for 1 hour. Having 1.3 microliters (thousandths of a milliliter) evaporated in your house would exceed the long term one-year ESL of 1.4 ppb 6. This is a good reason not to store portable gasoline containers in your attached garage. It takes only a tiny amount of benzene to exceed ESLs. Miscellaneous facts: Benzene evaporates 2.8 times faster than ether, and begins evaporating at only 12 F. 7 Benzene boils at 176 F, but freezes at 42 F. Benzene is flammable at temperatures down to 12 F. About 50% of people would be able to smell benzene if the level was about 2,700 ppb. Benzene can dissolve in water up to 0.8 grams per liter. This is equivalent to.91 ml/l. Benzene vapor is 2.7 times as dense as air. Benzene levels while pumping gasoline into a car: 11 ppm right next to the pump, down to 250 ppb 5 feet away. 8 Benzene is found in cigarette smoke 9 at concentrations in the neighborhood of 50 to 150 µg per cigarette Health Risks with Benzene Benzene is carcinogenic; the principal health risk for chronic exposure to benzene is leukemia. 12 Both acute myeloid leukemia (AML) and acute non lymphocytic leukemia (ANLL) are conclusively linked to benzene. Although some reports have linked benzene exposure to lymphatic tumors, the Centers for Disease Control (CDC) considers that link plausible but inconclusive. CDC says that at very high concentrations, benzene rapidly causes central nervous system depression, which can lead to death. Chronic exposure can cause anemia and other blood disorders, and possibly reproductive disorders Based on inhaling 11,000 liters of air per day: sq ft * 8ft = cubic meters * 4.50 micrograms = 1.53 milligrams *.879 specific gravity =.0013 ml = 1.3 microliters (American Journal of Public Health, May 1990, Vol. 80, No. 5) CDC Benzene Reference 13 EPA Benzene Reference 2

3 Benzene and Natural Gas Operations There are two major types of concern with regards to benzene and natural gas production: air pollution, and ground water contamination. Groundwater contamination with benzene has been documented, and is suspected to be related to hydraulic fracturing.14 The link with fracturing is hard to prove because federal laws exempt the fluids used in the practice from disclosure and regulation under the safe drinking water act.15 The State of Texas has no specific regulation of the practice, although some states do.16 Figure 1 - Tank Battery at DFW Natural Gas Site Benzene can become airborne from natural gas sites in the same way that other VOCs are emitted, typically from glycol dehydration units, or through evaporation from water or condensate tanks and expulsion from tank vents as water rises or by thermal expansion.17 Unlike general ambient benzene levels resulting from automobiles and fuel stations, which are relatively spread out, gas wells and their associated equipment and storage tanks represent point sources that could cause locally much higher levels to some down-wind receptors. Current TCEQ Permits by Rule (PBRs), allow oil and gas wells statewide to emit up to 25 tons per year of VOCs per facility, of which benzene is certainly a part.18 Proposed TCEQ rules, if passed, would lower that to 10 tons per year.19 Concerns about benzene in the air began to increase in early January of 2010, when a TCEQ study of Barnett Shale natural gas facilities in North Texas showed high levels of benzene near two natural gas sites, out of 97 sites surveyed, and 19 additional sites with levels higher than the TCEQ would like to see20. The TCEQ caused a firestorm of controversy by withholding information from the public. The agency was reassuring the public and local elected officials, even though the equipment used for the survey was not sensitive enough to detect benzene at long (p based on examination of Texas Administrative Code, Title 16, Part 1, Chapter 3) TAC section 106.4: ac=&ti=30&pt=1&ch=106&rl=

4 term screening levels. 21 Later lab results from the same survey showed benzene higher than the long term ESL at four Fort Worth locations, ranging from 1.9 ppb to 6.3 ppb. One of the sites had benzene at 1,100 ppb, and another at 15,000 ppb 22, well exceeding both the short-term (180 ppb) and long-term (1.4 ppb) ESLs, and into the range for acute health effects. These wells, operated by Targa Resources and Devon, across the street from each other, both had malfunctions that have been fixed. The TCEQ study was criticized both because of the problem with disclosure, and the quality of the measurements, made in the cold winter month of January, when VOC levels are likely to be at their lowest due to temperature. BSEEC Air Quality Study In June, the Barnett Shale Energy Education Council (BSEEC), an industry consortium funded by the top operators in the Barnett Shale, conducted its own air quality study in the Barnett Shale 23. The study, conducted by Titan Engineering chose sites in Fort Worth and Arlington predicted to have the highest amounts of pollution, based on production data and the type of facility. Titan took one-hour and 24 hour samples at eight well sites and two natural gas compressor sites, testing the samples for benzene, formaldehyde, sulfur compounds, and other VOCs. The BSEEC study found only one facility with benzene levels exceeding long-term ESLs: the Encana Mercer Ranch well site in South Fort Worth 24. The site, with 6 wells produces wet gas, and has a battery of 20 tanks for condensate and water. Sample locations within 100 to 150 feet from the tanks had 24 hour readings of 1.96 ppb and a one-hour reading of 3.15 ppb. Although these numbers exceeded long-term ESLs, the site in question was set back such that there were no protected uses within at least 1000 feet of the tanks. 25 Despite the finding, BSEEC said the results showed there are no harmful levels of benzene and other compounds being emitted from natural gas sites tested. Encana Site Demonstrates Deficiency in Lewisville Ordinance In Lewisville, our setback requirements would allow water and condensate tanks to be within 100 feet of a protected use like a home, school, church, or park. 26 As made clear from the study, it is possible for a facility to have levels exceeding the long-term ESL at that distance. While the location in question does produce wet gas, and Lewisville is expected to produce dry gas, there is no distinction or requirement in the ordinance based on the type of gas produced. It should be noted that Lewisville also has no specific requirements for setbacks from glycol dehydrators, which could presumably be on the edge of the property line arlington-district Lewisville Code of Ordinances, Sec (d)(2): tanks must also be at least 100 feet from any protected use or combustible structure 4

5 Figure 2 - Map showing Encana Mercer Ranch site with Lewisville setbacks superimposed Criticism of BSEEC Study This author read the BSEEC study (at least the parts provided to the public) and found the methodology and implementation to be fairly sound. In trying to find the sites considered to be worst-case scenarios, Titan classified sites by production levels, and sought input from the City of Fort Worth. The study aimed to place sampling canisters downwind from the sites, and used meteorological equipment to verify this. Quality control measures were implemented, although the final report excludes the quality control data and raw laboratory results. Sharon Wilson, of the Texas Oil and Gas Accountablity Project (OGAP) offered these criticisms of the study 27 : The company in charge of the study, Titan Engineering, is a favorite of operator Chesapeake Energy (CHK) and a company that works exclusively for the natural gas industry. The drillers all got fair warning before the testing occurred. Faith Chatham, of Dallas Fort Worth Regional Concerned Citizens (DFWRCC) also had several problems with the study 28, which we list here: Only one well of 187 in Arlington was chosen. Chatham thinks that is not a representative sample

6 Titan attributes high readings to off-site sources, but doesn t provide the data to justify it. Exposures are less than 14 days, not going far enough to determine what long-term exposure would be. Deborah Rogers of Fort Worth also posted some criticisms of the BSEEC study, a few of which we list here 29 : Ten sites were not nearly enough to be representative of the over 2000 sites within Fort Worth. Exclusion of sites undergoing flaring, venting, or fracking and only including completed sites is not representative of a worst-case scenario with benzene emissions. Although formaldehyde levels exceeded standards in 5 of 9 samples, Titan states the levels are not caused by a natural gas site, but did not identify the source. One site showed normal condensate production over the prior 30 days, but no production on the day of the sample. 30 Wind speeds were excessive at some sites, with gusts up to 37.5 mph at one time, could make those sites appear to be emitting less than they were, as any emissions would dissipate more quickly. In addition to Wilson, Chatham, and Rogers criticism, I would add a couple of things: The study was industry-funded and implemented, and not exactly covert. We are concerned that with knowledge of the study and the dates of sampling, operators might have incentive to take measures to temporarily reduce their emissions to levels lower than would be typical. For instance, an operator could perform extra maintenance prior to the study, or avoid certain activities or lower production levels while readings were being taken. Again, we are not saying this is the case, but the reading discrepancy with regards to condensate production found by Rogers should have been addressed in the analysis. We agree that it would be preferable to have some longer-term exposures, so that it would be possible to get a more representative reading of typical down-wind levels. The problem with this is that summa canisters don t lend themselves well to readings this long in duration. Sorbent tubes (unpressurized tubes containing material that absorbs airborne chemicals for laboratory analysis) are less accurate but some types can be used for sampling periods up to 30 days 31. Our Take That said, taking the survey even at face value, we conclude that the health risks associated with airborne benzene are real and quantifiable, but low, most of the time, given adequate setbacks from protected uses and vigilant surveillance for leaks and malfunctions. We do want to see more data, and we think it is prudent to monitor overall ambient levels of benzene, and do periodic surveys like this to check natural gas facilities. Given that long-term ESLs are very protective, if constant monitoring is done, then problems can be detected and repaired in plenty of time to avoid long-term exposure to benzene at higher levels. On the other hand, if the problem is ignored, people could be exposed to high levels at some sites Condensate production averaged.28 BPD, but 0 was shown in production data for sample day. Possibly the tank gauges do not show that precision

7 Based on an examination of the data and the studies, we find the following to be the aggravating and the mitigating factors for benzene. These could be used as the basis of ordinances or regulation designed to prevent the airborne release of dangerous amounts of benzene. Anything that is done to reduce benzene would also reduce the amounts of other volatile organic compounds, each of which may have its own or an additive toxicity, and all of which add to the ground-level ozone problem that the DFW area suffers. Aggravating Factors for Airborne Benzene High outside temperatures or tank temperatures wet gas production of condensate Low wind speeds, consistent wind direction Location down-wind (generally North in the DFW area) from the source Location close to the site and its tanks Greater number of tanks, greater tank surface area Unpressurized tanks No emissions controls installed Benzene used in well stimulation Leaks or open valves or hatches Infrequent monitoring by the operator Mitigating Factors for Airborne Benzene Low outside temperatures and tank temperatures Dry gas production little or no condensate just produced water 34 High wind speeds, variable winds Location up-wind or lateral to the site Location far from the site and its tanks Fewer tanks, smaller tank surface area Pressurized tanks Emissions controls installed Benzene not used in well stimulation Leak prevention and valves or hatches kept closed Frequent monitoring by the operator We hope this information is both enlightening and useful to you. Please do not hesitate to contact me if I can be of any assistance in further fact-finding. Updates or errata to this document will be posted on Permission to reprint is granted, provided that all notes and attributes are also included (Dallas-Fort Worth Ozone Non-attainment Area) 33 See article on WhosPlayin.com Dallas-Fort Worth Area Fails to Meet Ozone Attainment; Contingency Measures Implemented for more background: (TCEQ says benzene is still present, even in dry gas, though we acknowledge at lower levels) 7

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